Pyrolysis furnace having transverse mixing means in the end stacks

ABSTRACT

A regenerative pyrolysis furnace having dual combustion chambers and means for transverse flow in the end stacks of the refractory masses. These means for transverse flow in the preheat and quench tile stacks permit crossflow between the axial flow conduits, thereby minimizing the effects of plugging of these conduits due to carbon formation or shifting of tile.

United States Patent 1 Walker 1 Mar. 27, 1973 541 PYROLYSIS FURNACEHAVING 2,868,855 1 1959 Begley ..23 277 R x TRANSVERSE MIXING MEANS INTHE 2,473,427 6/1949 Hasche 2,936,162 5/ 1 960 Coberly ..263/51 ENDSTACKS Lynn P. Walker, Burghausen, Germany Inventor:

Marathon Oil Company, Findlay, Ohio Filed: Feb. 1, 1971 Appl. N0.:111,509

Assignee:

References Cited UNITED STATES PATENTS 12/1958 Begley et al ..23/277 R XPrimary Examiner-James H. Tayman, Jr. Attorney-Joseph C. Herring,Richard C. Willson, Jr. and Jack L. Hummel [57] ABSTRACT A regenerativepyrolysis furnace having dual combustion chambers and means fortransverse flow in the end stacks of the refractory masses. These meansfor transverse flow in the preheat and quench tile stacks permitcrossflow between the axial flow conduits, thereby minimizing theeffects of plugging of these conduits due to carbon formation orshifting of tile.

9 Claims, 4 Drawing Figures PATH-HEUumznm SHEET 10F 2 INVENTOR.

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INVENTOI? L. P. WALKER Fig. 3

SECTION A A' SECTION A-A' (alternate) A T TORNEY PYROLYSIS FURNACEHAVING TRANSVERSE MIXING MEANS IN THE END STACKS CROSS REFERENCES TORELATED APPLICATIONS 1970, all of which are assigned to the assignee ofthe present invention, relate to the general field of pyrolysis ofhydrocarbons.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to the field of hydrocarbon pyrolysis. Literaturerelating to this application will be found in Patent Classes 23-277,furnaces for analytical methods; 263-15, heating: with gas furnaceheaters; 263-51, heating: checker bricks; 260- 679, hydrocarbons:acetylene; and other related patent classifications.

2. Description of the Prior Art Processes for thermally crackinghydrocarbons into acetylene, ethylene, and other unsaturated gases havebeen described at length in the literature. (See, for example, the Wulffprocess described in U.S. Pat. Nos. 1,996,187; 2,037,056; 2,236,534;2,236,535; 2,236,555; 2,319,679; 2,518,688; 2,526,696; and 2,908,625.)The pyrolysis of methane, ethane, propane, butane and natural gas toform acetylene and ethylene have particularly been studied. (See, forexample, Tropsch and Engloff, Industrial and Engineering Chemistry, 27,p. 1,063 (1935) and U.S. Pat. No. 1,983,922.)

Various types of furnaces have been used for hydrocarbon pyrolysis. Thewell-known Wulff furnace will be used for exemplary purposes herein.This furnace is usually about feet long and contains five majorsections. Three of these sections are made of refractory tile (see U.S.Pat. No. 2,622,864 to Has che), often called l-lasche tile, and areoften referred to in the art as refractory masses. These refractorymasses contain axial flow channels, referred to in this application aslongitudinal conduits, through which the process flow stream istransmitted. Two larger sections of this tile form the right and leftendsections of the furnace and are commonly referred to as theendstacks. The third smaller refractory mass forms the center section ofthe furnace and is usually referred to as the center stack. Between thetwo end stacks and the center stack are two sections known as thecombustion zones, one on each side of the center stack. Thus, from endto end, the furnace consists of an end stack, a combustion chamber, thecenter stack, a second combustion chamber,.and the other end stack.Typically, such a furnace is operated in a cyclical fashion, that is,heating and cracking cycles are carried out in alternate left to rightand right to left flow patterns during operations.

The hydrocarbon feedstock is transferred through the end stacks throughnumerous parallel cylindrical grooves in the tiles which form conduitsrunning longitudinally through the tile stack. This provides properpreheating and quenching before and after the cracking reaction,respectively. However, due to the nature of the cracking reaction, cokeis readily formed in these conduits or tubes". This coke plugs certainof the tubes, thereby creating adverse temperature and pressuregradients within the furnace. As this problem becomes more severe, theefficiency of the process is decreased and the furnace must be shut downin order to decoke.

Another common fault of this furnace is the shifting of some of the tilestacks due to vibration and continual thermal expansion and contraction.This random shifting prevents flow through certain portions of the endstacks, thereby creating a similar problem as that when the spacesbecome plugged.

SUMMARY General Statement of the Invention According to the inventionthere are provided conduits for transverse flow among the longitudinalconduits in the refractory mass of each of the end stacks. For example,this may be a space formed by removing a transverse section of therefractory mass. This space can be equipped with baffles or not, asdesired.

The resulting tranverse flow alleviates the problem of pressure andtemperature gradients developed from the blocking of passages due tocoke formation or tile shifting. The existenceof this space providesmore evenly distributed flow patterns, resulting in a considerablylonger process run forthe furnace, and an increase in product yield.

Utility of the Invention The invention relates to the production of thecommercially well-known products of ethylene and acetylene whichprincipally find use as reactants in the synthesis of numerous organicchemicals and as fuels. (See Miller S. A., Acetylene: Its properties,Manufacture and Uses, Vols. 1 and 2).

The transverse mixing zone channels the process gases towardssubstantially all of the surface area of the inner portion of the endstack in substantially uniform proportions. The uniform distribution ofheat energy in the end refractory mass tends to prevent the problem ofovercracking in one area or undercracking in another. This results in ahigher product yield and longer runs between shutdowns for decoking thefurnace.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a detailed plan view of thefurnace.

FIG. 2 is a cross-sectional top view of the mixing space, containing abaffle means.

FIGS. 3 and 4 are cross-sectional end views of a refractory mass,illustrating typical arrangements for the interconnection of thelongitudinal conduits within the refractory mass.

Referring to FIG. 1, a pyrolysis furnace typically has a metal shellconsisting of a top 2, sides 4, and a bottom. Such shell enables thefurnace to be operated under vacuum conditions.

The shell is lined with fire bricks 6 for insulating purposes. Disposedwithin the channel created by the shell are left end stack ceramicmasses 8 and 10, a center stack ceramic mass 12, and right end stackceramic masses l4 and 16. The center stack is spaced from the end stacksso as to create the left 18 and right 20 combustion chambers. Locatedbetween the end stack masses 8 and 10 is transverse mixing space 22.Similarly, located between end stack masses 14 and 16 is a transversemixing space 24. The furnace is symmetrical and the typical productionprocesses employ a cyclical operation whereby gases are conducted fromright to left and, alternately, from left to right during the two cyclesof operation (when feed' gas is moving from right to left, the rightcombustion chamber and end stack are said to be operatingon theproduction or make cycle, while the left combustion chamber and endstack are operating on the product heat transfer or heat cycle. Theconverse is true when the feed gas moves from left to right).

Extending into the left combustion chamber 18 is a fuel injection means26 extending through the sides of the furnace. A similar fuel injectionmeans 28 is located in the right combustion chamber 20. The outer endsof these nozzles are connected to a suitable source of fuel (not shown).

The ceramic masses (or refractory masses) may be formed of ceramiccheckers as shown in Hasche Pat. No. 2,622,864. The checkers havesemi-circular grooves in their bases and are so arranged that when thecheckers are stacked they form in the ceramic masses longitudinalconduits. The cross-sectional area of these conduits represents about 20percent to about 30 percent of the total cross-sectional area of theceramic masses.

FIG. 2, a cross-sectional top view of the mixing space, illustrates oneof many baffle means which may be employed in transverse mixing spaces22 and 24 of FIG. 1. The height of these baffles may range from beingequal to their widths to being equal to the vertical dimension of themixing space.

FIGS. 3 and 4, both cross-sectional end views of a refractory mass,illustrate typical arrangements for the interconnection of thelongitudinal conduits within the refractory mass. As is readilyobserved, many variations of these arrangements may successfully beutilized within the scope of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The desired products of apyrolysis furnace, such as the Wulff furnace, are acetylene, ethylene,or other unsaturated chemical compounds or mixtures thereof, formed bythe pyrolysis of a suitable hydrocarbon in the furnace and by theprocess known to the art. A suitable hydrocarbon" is any hydrocarbonknown to the art to be capable when pyrolyzed of forming acetylene,ethylene, or other unsaturated chemical compounds. Methane, ethane,propane, butane, gas oil or other petroleum fractions, and unsaturatedhydrocarbons such as ethylene, butylene, and propylene, and gases suchas natural gas or refinery gases are among the many hydrocarbons whichfall within this definition. Also, both light and heavy naphthas serveas suitable hydrocarbons. The operating conditions of this example areas described in US. Pat. No. 3,024,094 to Coberly, Column 5, line 32 toColumn 8, line 29.

The pyrolysis process is usually run with more than one furnace, so asto permit continual production even when a particular furnace is shutdown" for maintenance. Proper valve and piping arrangements arewell-known to the art. See, for example, U.S. Pat. No. 2,956,864 toCoberly.

the adjacent refractory mass and a width of preferably about 0.01 toabout 5, more preferably about 0.1 to

about 3, and most preferably about 0.7 to about 1.5 of

the combustion chamber width.

The transverse mixing space can also be equipped with a bafflearrangement to facilitate the crossflow.

FIG. 2 illustrates a typical baffle arrangement. While the baffle meansshown in FIG. 2 provides good mixing, it is not intended that thisapplication be limited to that means. Many conventional means ofbaffling will also work quite well with the proposed invention, orbaffling can be eliminated if desired.

EXAMPLE The results obtained from the practice of this invention on afurnace,the dimensions of which are identical with those given in FIG.1, indicate an average increase in acetylene-ethylene yield of about 3.5percent compared to the same-furnace before the mixing space wasinstalled. The mixing spaces used in this example are identical withthose illustrated in FIG. 1, and are located so that the front surfaceof each space is 1,285 mm from end to respective end.

The following table, which provides the process operating conditionswhich existed during the experimentation, compares the results obtainedwithout the mixing space (trials 1 and 2) with the results obtained withthe mixing space (trials 3 and 4):

The furnaces of trials 3 and 4 were also able to remain onstream percentlonger than the furnaces of trials 1 and 2.

It should be understood that the invention is capable of a variety ofmodifications and variations which will be made apparent to thoseskilled in the art by a reading of the specification and which are to beincluded within the spirit of the claims appended thereto.

What is claimed is:

1. In an apparatus for hydrocarbon pyrolysis comprising a plurality ofregenerative pyrolysis furnaces each comprising a first and a second endrefractory mass having longitudinal conduits through which feed gas isintroduced for pre-heating and products are exited for coolingrespectively; and adjacent to and terminating each refractory mass, twocombustion chambers equipped for external injection of fuel therein; anda center refractory mass, separating the combustion chambers whereinfeed gases are cracked; the combination therewith of a means forproviding transverse flow of gases among at least a plurality of saidlongitudinal conduits of said end refractory masses, wherein said meansfor providing transverse flow comprises a transverse space having alongitudinal dimension of from about 0.9 to about 1.1 combustion chamberwidths and said transverse space is equipped with one or more baffles.

2. The apparatus of claim 1 wherein the center line of said space islocated about three combustion chamber widths from the center line ofits respective combustion chamber.

3. The apparatus of claim 1 wherein the cross-sectional area of saidspace is equal to the cross-sectional area of the adjacent refractorymasses.

4. The apparatus of claim 1 wherein said means for providing transverseflow consists of at least a plurality of transverse conduits connectingvarious longitudinal conduits.

5. The apparatus of claim 1 wherein said means for providing transverseflow consists of various transverse conduits connecting at least aplurality of longitudinal conduits.

6. The apparatus of claim 1 wherein the total crosssectional area of thelongitudinal conduits is about 20 percent to about 30 percent of thetotal cross-sectional area of the refractory masses.

7. The apparatus of claim 1 wherein the longitudinal conduits arecylindrical in shape.

8. The apparatus of claim 1 wherein each longitudinal conduit issubstantially equidistantly spaced from each adjacent longitudinalconduit.

9. Apparatus according to claim 1 in which said baffles consistessentially of a plurality of baffles extending from the wall of thefurnace toward the midpoint of the furnace in a direction substantiallytransverse to the direction of flow.

2. The apparatus of claim 1 wherein the center line of said space islocated about three combustion chamber widths from the center line ofits respective combustion chamber.
 3. The apparatus of claim 1 whereinthe cross-sectional area of said space is equal to the cross-sectionalarea of the adjacent refractory masses.
 4. The apparatus of claim 1wherein said means for providing transverse flow consists of at least aplurality of transverse conduits connecting various longitudinalconduits.
 5. The apparatus of claim 1 wherein said means for providingtransverse flow consists of various transverse conduits connecting atleast a plurality of longitudinal conduits.
 6. The apparatus of claim 1wherein the total cross-sectional area of the longitudinal conduits isabout 20 percent to about 30 percent of the total cross-sectional areaof the refractory masses.
 7. The apparatus of claim 1 wherein thelongitudinal conduits are cylindrical in shape.
 8. The apparatus ofclaim 1 wherein each longitudinal conduit is substantially equidistantlyspaced from each adjacent longitudinal conduit.
 9. Apparatus accordingto claim 1 in which said baffles consist essentially of a plurality ofbaffles extending from the wall of the furnace toward the midpoint ofthe furnace in a direction substantially transverse to the direction offlow.